WASHINGTON - A US naval ship and surveillance plane are heading to the Andaman Sea and Bay of Bengal to search for a missing Malaysian airliner that vanished a week ago, officials said.

US media reports, meanwhile, suggested the plane experienced marked changes in altitude after it lost contact with ground control, and altered its course more than once as if still under the command of a pilot.

A P-8 Poseidon aircraft and a guided missile destroyer, the USS Kidd, were due to aid the international hunt for the jet as the search effort extended further west, Pentagon spokesman Colonel Steven Warren said.

"At Malaysia's request, the USS Kidd is north of the Strait of Malacca in what we're calling the western search area," Warren told reporters in Washington.

The Kidd was preparing to search the Andaman Sea and the Bay of Bengal for the Malaysia Airlines plane.

"The P-8 will be searching a much larger search area... the southern portion of the Bay of Bengal and the northern portion of the Indian Ocean," Warren said, adding that final orders had yet to be issued.

The Boeing 777 vanished off the radar early Saturday over the South China Sea with 239 people on board, after taking off from Kuala Lumpur bound for Beijing.

The plane's fate has vexed investigators and Malaysian authorities have dramatically expanded the scope of the search operation.

In the latest twist, The New York Times, citing a preliminary assessment by a person familiar with the data, said radar signals recorded by the Malaysian military appeared to show the jet climbing to 45,000 feet (13,700 meters) -- above the approved altitude limit for a Boeing 777-200.

The radar track then shows the missing plane descending unevenly to an altitude of 23,000 feet, below normal cruising levels, as it approached the densely populated Malaysian island of Penang, the report said.

Then it turned from a southwest-bound course, climbed to a higher altitude and flew northwest toward the Indian Ocean.

The hunt had initially focused on the South China Sea east of Malaysia -- along the intended route of the jet.

But Malaysia's government was now looking at a vast area, extending to the Bay of Bengal and the Indian Ocean, with 13 countries now involved in the desperate search.

The Pentagon said a second naval destroyer, the USS Pinckney, which had assisted the search effort this week, was due to depart for Singapore for scheduled maintenance.

The P-8 aircraft now in the area was replacing a P-3 Orion surveillance plane that had taken part in the initial hunt for the airliner.

After flying over the Gulf of Thailand on Thursday looking for signs of plane debris, the P-3 reported "nothing found," Warren said.

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